口裡食了 Food In His Mouth
中間有座獅駝洞。洞裡有三個老妖，有四萬八千小妖，專在那裡吃人。我們若屣著他些山邊兒，就是他口裡食了。莫想去得。」中间有座狮驼洞。洞里有三个老妖，有四万八千小妖，专在那里吃人。我们若屣着他些山边儿，就是他口里食了。莫想去得。」
逐句解 Line by line
In the middle of it is the Lion Camel Cave.
Seven characters, repeated word for word from the old man's account. This part Bajie has got exactly right.
In the cave are three old demons and forty-eight thousand lesser ones, and their whole business there is eating people.
四萬八千 — forty-eight thousand. The old man said forty-seven or forty-eight; Bajie has rounded up, which is what fear does to a figure. 那 here is the locative nà, in that place.
If we so much as brush the edge of his mountain we are food in his mouth. There is no thinking of going on."
屣著 has 著 as zháo, the band of contact made — if we so much as touch it. That is the fourth reading of this character in the chapter and completes the set of bands the book actually uses. 口裡食 is food in the mouth, already swallowed as far as the grammar is concerned.
Bajie's report is accurate in its bones and wrong in its edges. The cave is right, the eating is right; the ridge has become a mountain and the total has been rounded up. Nobody corrects either.
The image he closes on is the good one. Not we will be eaten but we are food in his mouth — the thing already decided, the outcome spoken of in the present tense. It is how frightened people describe a danger they have not yet met.
And his conclusion is the same as the one he squatted down with. There is no thinking of going on. The whole errand, undertaken to establish whether the road was passable, has produced a recommendation to turn round.